The invention relates to a method for the input signal correction of a misfire detection function and for the cylinder equalization in an internal combustion engine, especially of a motor vehicle.
Methods for detecting combustion misfires by means of determining a rough running are known, if required, while considering filtered rough-running values. Likewise, methods for improving the quality of the combustion misfire detection, for example, by means of transducer wheel adaptations or general adaptations, belong to the state of the art. An optimization of the combustion misfire detection of this kind is known under the designation xe2x80x9cfuel-on-adaptationxe2x80x9d. The fuel-on-adaptation is based on rough-running values or segment times of the internal combustion engine and learns transducer wheel faults and torque differences between the individual cylinders during operation of the engine. When learning the transducer wheel faults and the torque differences, corrective values are formed by the fuel-on-adaptation with which the instantaneously present segment times or the rough-running values, are corrected. Here, only the input signals of a misfire detection function are changed. A correction utilizing the fuel-on-adaptation has no effect on the engine as can take place, for example, in the form of a torque correction via an injected quantity of fuel increased in a suitable manner.
In gasoline direct injection systems, a cylinder equalization functions to cancel torque differences of individual cylinders during the operation of the engine. Torque differences of this kind amongst the individual cylinders can, for example, occur because of scattered differences of individual injection valves, which are present (manufacturing inaccuracies which cannot be avoided) or these torque differences can occur because of valve coking. A control for cylinder equalization determines the torque deviations amongst the individual cylinders on the basis of rough-running values during the operation of the engine. The cylinder torques are preferably equalized in a stratified operation by adapting the cylinder-individual injection quantity of fuel in the form of a dynamic control. The cylinder equalization functions to correct for cylinder-individual correction of the injection times in dependence upon the cylinder torques which are adjusted in each case. The corrected injection times have, in turn, an influence on the cylinder torque. Accordingly, an effect of the injection times on the cylinder torque is present so that torque differences amongst the cylinders can be controllable to the value zero via the control for cylinder equalization.
It is disadvantageous that a trouble-free function of the fuel-on-adaptation and therefore a reliable misfire detection during operation of the engine is not ensured.
The method of the invention is characterized in that a control for input signal correction and a control for cylinder equalization are alternatively activated. In this way, it is ensured that the activated control for input signal correction (fuel-on-adaptation) is not negatively influenced by the simultaneous activation of the control for cylinder equalization. Such a disturbance of the control for fuel-on-adaptation is especially caused by the situation that a correction of the input signals of misfire detection functions takes place also on the basis of the cylinder torques which, in turn, are corrected by means of the cylinder equalization. The cylinder equalization thereby influences the fuel-on-adaptation via the cancellation of torque differences between individual cylinders by means of cylinder-individual correction of the injection times. This is so, because the fuel-on-adaptation corrects the input signals of misfire detection functions, inter alia, on the basis of the cylinder torques. A reliable misfire detection and simultaneously an effective cylinder equalization is ensured during operation of the engine because of the alternative activation of the control for input signal correction and the control for cylinder equalization. This is so because the control for fuel-on-adaptation can only be activated at a time point at which the control for the cylinder equalization is not activated and vice versa.
A cylinder torque correction takes place for cylinder equalization and is advantageously considered by the activated input signal correction control. A detection and consideration of a cylinder torque correction is ensured in a reliable manner for an activated input signal control because of the alternative activation of the two controls. The cylinder torque correction was initiated by the previously activated cylinder equalization control for cylinder equalization.
According to a first embodiment, the cylinder torque correction values of the input signal correction control are incorporated in corresponding input signal correction values. In this way, and by means of a direct and time-proximate computation of the cylinder torque correction values with the input signal correction valves, a continuously adapted input signal correction is maintained during the activation of the corresponding control.
According to a second embodiment, the particular cylinder torque correction value is maintained constant when the input signal correction control is activated until the difference between a pregiven desired value and an actual value of the cylinder torque correction exceeds a fixable threshold value whereupon a new constant actual value is adjusted to the pregiven desired value and the input signal correction control is reset. Here, the cylinder torque value of the particular poorest cylinder is applied for the actual value. The desired value is adjusted as a new constant actual value for all cylinders. The input signal correction control (fuel-on-adaptation) is reset to neutral start values because of the reset thereof. In this way, the fuel-on-adaptation starts the learning proceeding from neutral start values. After the reset of the fuel-on-adaptation, the thresholds of a misfire detection are increased and are only lowered again after advanced fuel-on-adaptation.
In an advantageous manner, the cylinder equalization control adjusts the injection time at least for the next combustion for each cylinder in dependence upon the cylinder torque, which adjusts after each combustion. In this way, a reliable and effective cylinder equalization is ensured during the operation of the engine.
It is advantageous that the input correction forms corrective values for adjusting the input signals of at least one misfire detection function for each cylinder individually in dependence upon the degree of rough running and/or the segment times. In this way, the quality of the combustion misfire detection is improved or optimized in a reliable manner.
Preferably, the activation of the input signal correction control and the cylinder equalization control takes place via an alternative switching unit. Alternative switching units permit an alternative activation of the control for the input signal correction and the control for cylinder equalization in a reliable, rapid and automatic manner.
Additional advantageous configurations of the invention become evident from the description.